1. Field of the Invention
This invention relates to a rotary magnetic head drum assembly for a helical scanning type magnetic recording-reproducing device, particularly designed so that the axial dimension of the rotary head drum assembly is as small as possible.
2. Description of the Prior Art
FIG. 1 shows an example of the conventional magnetic head drum assembly in section. In case of the conventional head drum assembly, as is shown in FIG. 1, the rotary head drum 1 is borne on the rotation axle 12 by means of ball bearings 6 and 7 in such a manner that the rotary head drum assembly 1 is arranged above the bearings, while the driving rotary magnet 8 is arranged beneath the bearings. A support member 3 for the primary coil 4 of a rotary transformer is arranged at the side of the rotary drum, while a secondary coil 5 of the rotary transformer is arranged at the side of the stationary drum. Further, beneath the bearings the rotary magnet 8 is arranged at the side of the rotary drum by means of a support member 11, while in order to drive the magnet 8 in rotation a stator 9 and a stator coil 10 are arranged at the side of the stationary drum. 14 is a magnetic head arranged on the rotary drum 1 by means of the base plate 13, the output of which head is connected to the primary coil 4 of the rotary drum by means of a conductor (not shown) so as to be electromagnetically coupled with the stationary transformer (the secondary coil). The recording-reproducing magnetic tape runs slanted along the surface of the rotary drum and the stationary drum in such a manner that during scanning with the rotary head the track is formed slanted on the surface of the tape.
In case of the conventional drum assembly as is shown in FIG. 1, because the rotary drum is mounted on the rotation axis and the bearings 6 and 7 exist between the stationary drum and the rotary drum, it is difficult to obtain a rotation with high accuracy when the distance between the bearings is small and it is thus difficult to realize a drum assembly which is thin along the axial direction, which is disadvantageous.